Processes for making blends of co-cured and self-curable rubbers, where one of the curable rubbers does not have halogen functionality, are taught in the above-identified copending patent applications. The term "plastic" refers herein to a resin selected from the group consisting of polyamides, polycarbonates, polyesters, polysulfones, polylactones, polyacetals, acrylonitrile-butadiene-styrene (ABS), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), styrene-acrylonitrile (SAN), polyimides, styrene-maleic anhydride (SMA) and aromatic polyketones, any of which may be used by itself or in combination with another. Most preferred are polar engineering thermoplastic resins, e.g. polyamides and polyesters.
Ser. No. 08/686,782 teaches that acrylic rubbers having "reactive" functional groups may be self-cured without a curing agent. Such "reactive" functional groups are so characterized because it was found that they will crosslink, albeit slowly, under typical dynamic vulcanization conditions, usually in less than 5 minutes, without either a curing agent or an accelerator. "Dynamic vulcanization conditions" refer to a temperature high enough to maintain the components in a liquid state, mixed with high enough shear energy provided for a period long enough, and at a rate sufficient to produce a sudden increase in torque indicative of crosslinking; the temperature ranges from 180.degree. C. to 260.degree. C., preferably 220.degree. C.-240.degree. C., and the shear energy is in the range from about 0.01 to 1 Kw-hr/lb, which covers both batch mixers and continuous extruders. Details of conventional dynamic vulcanization are set forth in U.S. Pat. No. 4,141,863 to Coran and Patel, the disclosure of which relating to dynamic vulcanization is incorporated by reference thereto as if fully set forth herein. Such rubbers were therefore stated to be "self-cured" under dynamic vulcanization conditions. A rubber having a vinyl chloroacetate group was used as a control; it was cured (alone, and not as a co-reactant with another functionalized rubber) with a quaternary ammonium salt, to illustrate properties of a typical, desirable TPV. Table I presents an illustrative example in which the control is an acrylic copolymer having halogen functionality (AR-71) cured with a quaternary ammonium salt (example 1); one of the repeating units of the copolymer has a functional group with a halogen substituent. Another such functional group is benzylic chloride. Such rubbers are hereinafter referred to as having "halogen functionality" or "AcrRubHal", for brevity. By "halogen functionality" is meant a reactive cure site containing a halogen selected from the group consisting of fluorine, chlorine, bromine and iodine, most preferably chlorine. Other illustrative examples in Table I of the '782 application present formation of TPVs from rubbers with epoxy and carboxyl groups without the necessity of a curing agent, using a metal stearate as an accelerator. Examples 2-7 teach combinations of acrylates with epoxy (AR-31 or AR-53) and carboxyl (Vamac-GMB) groups cured with magnesium oxide. Table III illustrates the formation of a vulcanizate of two rubbers, one having a carboxyl group (Vamac-GMB which contains a 0.09 phr antioxidant package) and the other rubber having a hydroxy group (Hytemp 4404 available from BFGoodrich Company) (see examples 8-10 and 12-15). Example 11 illustrates a TPV formed from rubbers having reactive epoxy and hydroxy groups. All examples 8-15 are self-cured with either potassium or magnesium stearate. Table V illustrates the formation of vulcanizates from other rubbers having the above-identified functional epoxy, carboxyl and hydroxy groups, and each is self-cured with potassium stearate. When one group is one of the foregoing groups and the other group has halogen functionality, the rubbers do not self-cure.
The '798 and '799 applications teach TPVs formed by a process in which a first curable acrylic rubber and a curable terpolymer are vulcanized in a polyamide and a polyester respectively, in the presence of a curing agent, to form a blend which has a single low temperature brittle (LTB) point which is intermediate the LTBs of the constituent rubbers.
In the '798 application, an ethylene-alkyl acrylate-carboxylic acid terpolymer rubber is co-cured in a polyamide with another functionalized acrylic rubber using a curing agent, and also in the presence of an accelerator such as a metal stearate. Table I presents illustrative control examples #s 1 and 3 with Nipol AR90-130A having a carboxyl group obtained from Nippon Zeon, which are cured with an amine-terminated polyether. Combinations of the Nipol with the terpolymer rubber are similarly cured. Other illustrative examples #s 5-7 in Table I present formation of TPVs from the rubbers using no curing agent, indicating the reactivity of the epoxy and carboxyl groups is sufficient to permit crosslinking without a curing agent. In Table II, TPVs of the terpolymer and a rubber with hydroxy functionality (Hytemp 4050 from BFGoodrich) are all cured with hexamethylene diamine carbamate.
In the '799 application, an ethylene-alkyl acrylate-carboxylic acid terpolymer is co-cured with another functionalized acrylic rubber with a curing agent, and also in the presence of an accelerator such as a metal stearate. As before, a rubber having a vinyl chloroacetate group was used as a control, cured with a quaternary ammonium salt (but not as a co-reactant with another functionalized rubber), to illustrate a typical desirable TPV. Table I presents an illustrative example in which the control is AcrRubHal (AR71) cured with a quaternary ammonium salt (example 1). Other illustrative examples in Table I present formation of TPVs from different rubbers with carboxyl groups (similar functionality) using magnesium oxide as a curing agent, and a metal stearate as an accelerator. Examples 2-8 and 11-16 teach combinations of different acrylates (Vamac-G and R-40-130A from Nippon Zeon) with similar carboxyl groups cured with magnesium oxide and other curing agents, most using a metal stearate as accelerator. Illustrative examples 17, 19 and 22 present a TPV formed from reactive carboxyl and epoxy functional groups; and #23 presents a TPV formed from reactive carboxyl and hydroxy functional groups, using only potassium stearate as accelerator. There is no teaching that a AcrRubHal can be co-cured with any one or more of the others with the curing agents taught.
In numerous applications, a AcrRubHal provides particularly desirable properties when it is cured with another curable acrylate rubber having carboxyl, hydroxy, or epoxy functionality (singly or together referred to as "AcrRubX"). To date, tailored TPVs of "plastics" having a combination of (AcrRubHal+AcrRubX) dispersed therein are vulcanized sequentially with a curing agent, typically a quaternary ammonium salt. The vulcanization is generally accelerated with a metal fatty acid salt, typically a metal stearate or oleate. For example, when Horrion in U.S. Pat. No. 5,589,544 used a combination of rubbers, one of which had halogen functionality, he cured first one group, then the other in a two-stage process. He therefore never co-cured and crosslinked the halogen-containing group with another non-halogen-containing group (e.g. carboxyl).
The curable rubbers in a TPV are compatible with each other and also with the engineering plastic. By "compatible" is meant that the rubbers form a mixture in which a second phase can co-exist with the continuous phase without the use of a compatibilizer or a surface active agent. Typical acrylic rubbers have a repeating unit with a C.sub.1 -C.sub.10 alkyl group in combination with a repeating unit having a group chosen from carboxyl, hydroxyl, epoxy, halogen, ester and the like, and may also include a repeating unit of a C.sub.2 -C.sub.3 olefin. Acrylate rubbers which include a repeating unit derived from a monoolefinically unsaturated monomer which does not have a curable functional group (or reactive site), e.g. ethylene-methyl acrylate copolymer, are not "curable rubbers" as the term is used herein. Because a TPV is formed by melt-blending at a temperature in the range from about 200.degree. C. to 250.degree. C. the reactivity of each component of the blend in that temperature range with one or more of the other components, determines the properties of the final blend.
However, to custom-tailor a blend for requires searching for and finding specific combinations of acrylate rubbers which will provide those properties, and to cure them in such a manner that the effect of the curing agent does not detract from those properties.
One option is to provide different functional groups in the chains of a single rubber and inter-cure these groups as is done in Hytemp.RTM. rubbers having both carboxyl and halogen functionality. Since a combination of acrylate rubbers, each having at least one different functional group, provides a wider selection of repeating units from which one may strive to tailor a blend with specific sought-after properties, such a combination is a preferred choice. Whichever combination is chosen, because of the elevated processing temperature, to minimize the adverse effects of a curing agent, particularly if there is a tendency to evolve toxic organic byproducts. Optimally, the final blend is produced by curing without any curing agent. This is possible when the functional groups are co-reactive, that is, they react under elevated temperature conditions sua sponte, that is, on their own or "self-cured", as is the case between a rubber with an epoxy group and another rubber, particularly those with carboxyl, hydroxyl or amino functionalities, as taught in the aforementioned copending applications. An optimal solution to the problem would provide the desired cure with a curing agent which has minimal adverse effects attributable to it, with respect to the other components, and particularly without generating toxic byproducts. More particularly, it is desired to cure plural rubbers with different functional groups at least one of which has a halogen substituent, with a single curing agent which does not produce toxic byproducts and does not adversely affect the desirable properties of the finished, cured blend in which the plastic is not cured.
Highly desirable properties are obtained in a cured blend when one of the rubbers has halogen functionality. Curing such a combination typically requires multiple curing agent which tend to produce toxic byproducts, and also tend to introduce undesirable properties contributed by the curing agents. Further, commonly used curatives such as a quaternary ammonium salt or a tertiary amine in combination with a metal stearate, have been found to produce byproducts harmful in excessive quantity, when used to cure plural rubbers one of which has halogen functionality.
Carboxyl and halogen functional groups in a single chain of an acrylate rubber are dynamically vulcanized ("cured" for brevity) with a combination of a quaternary ammonium salt or a tertiary amine and potassium stearate in commercially available Hytemp.RTM. rubbers. Surprisingly, the combination of a quaternary ammonium salt and potassium stearate, or, a tertiary amine and potassium stearate has so minimal a curing effect to cure a AcrRubHal with another rubber having carboxyl, hydroxyl or epoxy functionality, that no substantial crosslinking is evident as indicated by the relatively low torque generated (during blending for vulcanization). Potassium stearate, alone, is not recognized as an effective curing agent for a thermoset acrylate rubber or ethylene acrylic rubber.